Corrosion-resisting cobalt-chromium-tungsten alloys



United StatesPatentQ No Drawing. Filed June 2, 1964, Ser. No. 372,089 .I

Claims priority, application Austria, June 4,

A 4,457/63 2 Claims. (Cl. 75134) Cobalt-chromium-tungsten alloys having a high abrasion resistance and high-temperature stability and, containing a relatively large amount of carbon consistin their as-cast and as-welded conditions substantially of a large amount of hard chromium-tungsten carbides, which are embedded in a non transforming, cubic face-centered, tough cobalt-chromium matrix. The cooperation of the hard carbides and the tough matrix is responsible for the high abrasion resistance and high-temperature stability of these alloys. The two main constituents of the structure are also decisive for the corrosion behavior. Whereas the carbides are hardly susceptible to hydrochloric acid and sulfuric acid, these acids attack the cobalt-chromium matrix. As the matrix is dissolved out of the structure, the carbide lattice loses its coherence and can readily be detached by mechanical means from the core which has not yet been attacked. Hence, the resistance to corrosion can be improved only by an improvement of the resistance of the matrix in which the carbides are embedded.

The present invention provides cobalt-chromium-tungsten alloys which contain additions of copper and, if desired, molybdenum, for a substantially increased resistance to corrosion. Two alloys having the following composition have been prepared bymelting:

TABLE l.CHEMICAL COMPOSITION OF COBALT-CHROM- IUM-TUNGSTEN ALLOYS WITHOUT AND WITH COPPER AND MOLYBDEN UM It is apparent from Table 2 that the resistance to corrosion is much improved by the addition of copper and molybdenum.

- denum and copper.

TABLE 2.-WEIGHT LOSS OF THE COBALT-CHROMIUM- TUNGSTEN ALLOYS OF TABLE 1 IN HYDROCHLORIC lsilIfilfiURIC ACIDS, IN GRAMS PER SQUARE METER 7 All 10 percent hydrochloric acid 20 percent sulfuric acid oy Number Room tem- Boiliug tem- Room tem- Boiling perature perature perature temperature The weight losses of the alloy which contains molybdenum and copper are at room temperature about one fifth of those of the alloy 'which does not contain molyb- The test in boiling sulfuric acid "shows particularly that the weight loss is reduced to about one hundredth by the joint presence of copper and molybdenum. The improved corrosion behavior due to copper and molybdenum has been confirmed by electrochemical measurements carried out on these alloys in IN sulfuric acid at room temperature.

To find out whether a further increase in the resistance to corrosion can be achieved by larger additions of copp er and molybdenum, -a number of alloys having the composition indic-ated in Table 3 were prepared by melting.

TABLE 3.--CHEMICAL COMPOSITION OF COBALT-CHRO MIUM-TUNGSTEN ALLOYS CONTAINING COPPER AND MOLYBDENUM Alloy C Si Mn Cr W Go 1 Mo Cu Fe Number Calculated as the balance.

For a greater latitude regarding the addition of copper and molybdenum, the tungsten content of these melts TABLE 4.WEIGHT LOSS OF THE COBALT-CHROMIUM-TUNGSTEN ALLOYS OF TABLE 3, IN AS-CAST AND AS-WELDED CONDITION, IN HYDROCHLORIC ACID AND SULFURIC ACID, IN GRAMS PER SQUARE METER PER HOUR Content l0-percent hydrochloric acid 20-percent sulfuric acid Alloy Number M 0 Room temperature Boiling temperature Room temperature Boiling temperature As-cast As-welded As-east As-welded As-east As-welded As-cast As-welded These alloys were tested for weight losses in the form of welding rods and of samples of welds made from such r-ods. Table indicates the weight losses of samples of welds of conventional oobalt-chromium-tungsten alloys under corresponding conditions. A comparison of the weight losses indicated in Tables 4 and 5 shows the superiority of the alloys which contain copper, or copper and molybdenum, over the conventional alloys.

the fine structure show that the addition of copper and molybdenum does not appreciably aflfect the amount and nature of the precipitated carbides. The added copper and molybdenum are enriched mainly in the matrix to improve its resistance to corrosion.

An adverse efiect of copper and molybdenum on the abrasion resistance and high-temperature stability is not to be expected. The Rockwell C hardness numbers of the TABLE 5.CHEMIOAL COMPOSITION AND WEIGHT LOSS IN GRAMS PER SQUARE METER PER HOUR IN HYDROCHLO RIG ACID AND SULFURIC ACID OF CONVENTIONAL COBALT-CHROMIUM-TUNGSTEN ALLOYS IN AS-WELDED CONDITION Percentage content of Hydrochloric acid Sulfuric acid C Si Mn Cr W Go 1 B Nb Fe Room Boiling Room Boiling temp. temp. temp. temp.

1 Calculated as the balance.

It is also apparent from Table 4 that alloys 6 and 7 having the highest contents of copper and molybdenum do not have a higher resistance than the alloys 4 and 5 having lower contents of these elements. It is believed that the optimum composition of a cobalt-chromiumtungsten alloy having a high wear resistance and an increased resistance to corrosion, particularly by sulfuric acid :and similar media which do not have a very strong reducing action, is within the following limits:

22-25% C, 30-32% Cr, 13-20% W, 39-47% Co, up to 1% Mn, up to 1% Si, 0.3-6% Cu, and, if desired, up to 6% Mo.

The following alloy composition has proved particularly favorable:

2.2% C, 1% Si, 1% Mn, 30% Cr, 14% W, 46% CO,

4% Mo, 2% Cu.

By the attack of acids on the alloys, the matrix is dissolved out first so that the carbide remains on the sample alloys indicated in Table 3 are between 52 and and increase with increasing contents of copper and molybdenum.

It is also known that the high-temperature hardness of cobalt-chromiumdungsten alloys is improved by an addition of molybdenum up to 4% so that molybdenum results in an improvement of two important properties of the alloy.

What is claimed is:

1. A corrosion-resisting cobalt-chromium-tungsten alloy consisting essentially of 2.22.5% c-arbon, 30-32% chromium, 13-20% tungsten, 39-47 cobalt, up to 1% manganese, up to 1% silicon, 0.36% copper and up to 6% molybdenum.

2. A corrosion-resisting cobaltchromium-tungsten alloy consisting essentially of 2.2% carbon, 30% chromium, 14% tungsten, 46% cobalt, 4% molybdenum, 2% copper, up to 1% manganese, and up to 1% silicon.

References Cited by the Examiner UNITED STATES PATENTS 2,299,871 10/1942 Baird -171 2,309,372 1/1943 Wissler 75-171 2,553,609 5/1951 Schmidt 75171 2,695,844 11/1954 Clarke 75-171 FOREIGN PATENTS 809,088 2/ 1959 Great Britain.

DAVID L. RECK, Primary Examiner.

R. O. DEAN, Assistant Examiner. 

1. A CORROSION-RESISTING COBALT-CHROMIUM-TUNGSTEN ALLOY CONSISTING ESSENTIALLY OF 2.2-2.5% CARBON, 30-32% CHROMIUM, 13-20% TUNGSTEN, 39-47% COBALT, UP TO 1% MANGANESE, UP TO 1% SILICON, 0.3-6% COPPER AND UP TO 6% MOLYBDENUM. 